<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>*{
    padding:0;
    margin: 0;
    list-style: none;
}#app{
    width:100px;
    height:100px;
    background:red
}</style>
</head>
<body>

    <div id="app"></div>
    <script>alert('hello');</script>
</body>
</html>